I think a dedicated area for open world PVP could be very fun. This could be a cool way to reintroduce factions back into the game as well, because they could split the players into teams based on the faction they pick to represent in the Open world PVP zone and allow the player to return to their faction vendor for rewards for participating.
instead of just a dedicated zone for Open world PVP, you could even rotate it weekly like you do the flashpoints currently, with a certain planet being the "hot zone" for the week to keep things fresh and create a "map pool". This might actually be a lot more fun, because it would keep the players visiting all the planets. As incentives for doing this, you could make material gains doubled as well as progression for bounties and other things of that nature to add to making it worth going into.
I think this is probably a big suggestion so i dont know if it could be possible to work into D2, but hopefully this will make it to the team as a possible idea for D3.